The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A zeolite is a crystalline aluminosilicate having a framework based on an extensive three dimensional network of oxygen ions. The fundamental building block of all zeolites is a tetrahedron of four oxygen anions surrounding a small silicon or aluminum ion. These tetrahedra are arranged so that each of the four oxygen anions is shared in turn with another silica or alumina tetrahedron. The crystal lattice extends in three-dimension, and the −2 charge, i.e., oxidation state, of each oxygen anion is accounted for. Each silicon ion has its +4 charge, balanced by the four tetrahedral oxygen anions, and the silica tetrahedral are therefore electrically neutral. Each aluminum tetrahedron has a −1 residual charge since the trivalent aluminum is bonded to four oxygen anions. This residual charge is balanced by cations that occupy non-framework positions and act as strong, acid-donating Brønsted sites as further described in the schematic below and in Molecular Sieves: Principles of Synthesis and Identification authored by R. Szostak, 2nd edition, Blackie Academic and Professional, London, 1998.
            M              n        /        m                    m        +                                                  Non            ⁢                          -                        ⁢            framework                                                cation                      ·            [                        Si                      1            -            n                          ⁢                  Al          n                ⁢                  O          2                    ]        Framework    ·                              n          ⁢          H                2            ⁢      O              absorbed      ⁢                          ⁢      phase      
High-silica containing zeolites or molecular sieves are typically prepared from an aqueous reaction mixture containing sources of an alkaline metal or an alkaline earth metal oxide; sources of an oxide of silicon; optionally sources of aluminum oxide; and a cation derived from 1-Adamantamine, its derivative N,N,N-trimethyl-1-adamantamonium hydroxide, and mixtures thereof. Fumed silica is used as the typical source of silicon oxide, while aluminum hydroxide is used as the typical source of aluminum oxide. The “as synthesized” crystalline zeolite formed by crystallization may then be subjected to further treatment. For example, the structure directing agent (SDA) can be removed by thermal treatment (i.e. calcination). Such further treatments include the removal of the metal cation by ion-exchange using known methods such as using a diluted acid solution or ammonium nitrate solutions.
Y. Nakagawa et al, in Microporous and Mesoporous Materials, 22 (1998) p. 69-85 have computationally determined five different zeolites that can be made using the N,N,N-trimethyl-1-adamantamonium cation. Their molecular modeling calculations agree with their experimental data. They have reported that this template crystallizes SSZ-13, SSZ-23, SSZ-24, SSZ-25, and SSZ-31 type of zeolites. They show the crystallization field boundaries for the five zeolites commonly made by two SDA's. N,N,N-trimethyl-1-adamantamonium SDA molecule crystallizes chabazite phase at SAR 10-40, while STT phase at SAR 50-70.
Very few organic templates will produce structures similar to that of the SSZ-23 type zeolite. U.S. Pat. No. 4,859,442 discloses the preparation of crystalline SSZ-23 zeolite using adamantine quaternary ammonium ion as a template. The SSZ-23 zeolite so prepared has a mole ratio of an oxide selected from silicon oxide, germanium oxide, and mixture thereof to an oxide selected from aluminum oxide, gallium oxide, iron oxide, boron oxide and mixtures thereof greater than about 50:1.